The invention relates to a sleeper or support frame for a track system for railborne vehicles, particularly for a ballasted track.
A rail system sleeper frame having cross-ties interconnected with longitudinal supports is shown in the document CH 545 376. Contrasting to the ballasted track with cross-ties commonly used, sleeper frames have the advantage that they rest in the ballast more uniformly, that the ballast is subjected to less compressive forces under the wheel loads, and that they have an increased resistance to crosswise displacement.
The increased length of the sleeper frames in the longitudinal direction of the track, however, also leads to some disadvantages. One such disadvantage relates to the connections forming the transverse joints. In order to avoid detrimental movements of the transverse joints between the sleeper frames, the joints have to be connected by force-locking. Also, because of the little deformations of the frame in the ballast, the required elastic subsidence of the rail in the vertical direction under the wheel rolling over it makes highly elastic bearing or support constructions between the rail and the sleeper frame necessary, which, on the other hand, also promote the undesired tilting of the rail in the rail fixture. Furthermore, the regular and comparatively small distance of cross-ties and rail fixtures in the longitudinal direction of the track leads to vibrations in the ballast under the load of rolling wheels, which worsen the stability of the ballasted track considerably.
The disadvantages of this constructions are primarily the great technical and economic efforts required for the connection of the joints.
Furthermore, a permanent way is known from the document AT-PS 377 806 in which individual frame elements are arranged in a row, with each rail resting on one frame element by means of several bearings. The frame elements may be connected at their faces by means of plugs in order to absorb larger transverse forces. These elements manufactured in the style of prestressed concrete are reinforced by prestressing elements which extend in a straight line between two opposite faces of the element, respectively.
This construction has the disadvantage that, for absorbing large transverse forces, it is necessary to connect the frame elements, as well, which involves corresponding efforts regarding the manufacture and the assembly thereof. Furthermore, as a result of the relatively large distance of the rail bearings within one element, vibrations are caused when the load of the wheel of a railborne vehicle acts on the rail, because the bending behaviour of the rail varies. Manufacturing the element as a prestressed concrete part with reinforcement elements extending in the longitudinal and the transverse directions, respectively, makes prestressing in two directions perpendicular to each other necessary. This leads to considerable efforts in the manufacturing process, too.
The object of the present invention is to provide a sleeper frame for a track system for railborne vehicles, particularly for a ballasted track, in which it is not necessary even in case of large transverse forces to provide any large-scale connections of the sleeper frames in the transverse joints or any highly elastic rail bearings in the area of the rail fixtures, and which makes it possible to reduce the frequency of the vibrations generated in the railborne vehicle. Furthermore, it is intended to provide a simple and cost-efficient method of manufacturing sleeper frames of this kind.
The particular advantages of the sleeper frame according to the invention consist in that, on the one hand, the rail fixtures positioned outside on the edge of the frame reduce the vertical gaps in the transverse joint to such an extent that a connection between the sleeper frames can be dispensed with; on the other hand, the distance between the rail fixtures is made substantially larger thereby, which has the consequence that the frequency of vibrations is reduced correspondingly.
According to an embodiment of the invention, the outer rail bearings exhibit a large stiffness in the area of the rail fixtures and the intermediate rail bearing exhibits little, or relatively less stiffness, with the bearing surface of the intermediate rail bearing in a relaxed condition lying markedly higher than that of the outer rail bearings before the rail has been mounted, so, when the rail fixtures are tightened to secure the rail, the intermediate rail bearing is pressed down to the height of the outer rail bearings and is thus precompressed.
This results in the advantage that what is referred to as the lifting wave of the rail, which is encountered behind a wheel of the railborne vehicle in the direction of motion, is nevertheless supported by the intermediate bearing, so the rail is not lifted off the bearing in the area of the lifting wave. The damping effect of the elastic intermediate bearing is maintained.
According to another embodiment of the invention, an elastic material, preferably an elastic mat, is provided at the underside of the cross-ties and/or the longitudinal supports.
By this, it is achieved that the elastic mat arranged beneath the sleeper frame takes over the required vertical subsidence of the rail to a large extent, so the rail can be fixedly connected with the sleeper frame and can be protected from tilting with the aid of the stiff outer rail bearings. Owing to the soft intermediate rail bearing, the vertical rail deformation between the rail fixtures remains almost unimpeded.
The precompression in the intermediate rail bearing can be adjusted depending on its stiffness and the height of precompression in such a way that the vertical subsidence of the rail under the load of a wheel becomes equally large both in the middle of the frame and in the rail fixtures and thus corresponds to a continuous rail bearing. This also further improves the damping of vibrations of the system.
According to a different embodiment of the invention, a longitudinal support is provided under one rail axis, respectively. Hereby, a continuous or quasi-continuous bearing for the rail can easily be achieved without having to arrange the cross-ties very close to one another, for example. In particular, the number of cross-ties can be reduced to two. On this occasion, it is to be remarked that a quasi-continuous bearing of the rail means a bearing thereof in points or portions arranged close to one another, without a substantial deviation from the desired bending curve of the rail under load being created in the portions in which no bearing is provided.
The position of the outer rail bearings and/or the rail fixtures is selected such that the mid-plane of the rail fixtures transverse to the extension or longitudinal axis of the rails is spaced from the outer delimitation or nearest longitudinal end of the sleeper frame by a distance of xe2x89xa615 cm, preferably xe2x89xa610 cm in the longitudinal direction. Provided that the cross-ties have a corresponding dimension in the longitudinal direction, it is possible to arrange these elements in the middle of the cross-ties relative to this dimension, that is, the rail fixtures may be placed on the longitudinal center axis of the cross-ties.
According to the preferred embodiment of the invention, the cross-ties and the at least one longitudinal support are integrally formed, preferably as an element of prestressed concrete. Thus, simple and efficient manufacture is possible.
The sleeper frame as a whole may be configured as a part of prestressed concrete, or outer portions of the cross-ties (and, as the case may be, the longitudinal supports) manufactured as normal concrete parts or parts of prestressed concrete may be connected with a connecting rod in the form of a metal section.
According to an embodiment of the invention, prestressing elements are used as a reinforcement of the sleeper frame, which are anchored at the faces of a cross-tie. The prestressing elements are guided from this cross-tie via a longitudinal support to a second cross-tie using arcs and are anchored at the faces of this second cross-tie. This has the advantage that prestressing can be effected from merely two opposite sides of the frame and that this prestressing can be effected both in the longitudinal and in the transverse direction in one step.
Here, at least two U-shaped prestressing elements rotated by 180xc2x0 relative to each other may be provided, whose ends are anchored at opposite faces of two cross-ties, respectively. The arcs of the prestressing elements may extend through the same longitudinal support or, in case of two or more longitudinal supports, through one longitudinal support, respectively, which is closer to those faces of the cross-ties in which the ends of the respective other prestressing element are anchored.
However, the prestressing elements may also be configured to be substantially Z-shaped, with the ends of one prestressing element being anchored at respective opposite ends of different cross-ties. In a sleeper frame which comprises at least two longitudinal supports, at least four Z-shaped prestressing elements may be provided, with two Z-shaped prestressing elements intersecting in the same longitudinal support, respectively.
For producing a sleeper frame of this kind, this sleeper frame may first be manufactured with prestressing joints in the longitudinal supports. The prestressing elements are then prestressed by widening the prestressing joints. Finally, the prestressing joints are closed with a suitable hardenable building material so that a positive and a non-positive connection is obtained in the prestressing joints. Of course, another suitable type of fixing of the prestressed position of the sleeper frame may be employed, too.
These features relating to the specific reinforcement of the sleeper frame and the prestressing method may of course also be used independently of the features relating to the positioning of the rail fixture and the configuration of the bearings. In this way, conventional sleeper frames consisting of at least two cross-ties and one or several longitudinal supports may be manufactured easily and cost-efficiently, too.
These and other objects, advantages, and features of the invention will be apparent from the following description of the preferred embodiments, considered along with the accompanying drawings.